My [34F] husband [39M] thinks my new friend [37F] is responsible for his dog's death.

Sorry, this is kind of a doozy.
My husband Frank and I have been together for 6 years, married for 3. We met in a big east coast city (let's call it New Duckburg) and lived there for 4 years, before he was offered a really big job opportunity in the small midwestern city he grew up near (let's call it Corn City. He grew up in the suburbs of Corn City and moved there when he turned 18 for college. He lived there until he moved to New Duckburg in his late 20s). We moved to Corn City together a year and a half ago.
Ever since we moved here, I've had trouble making friends. The area is very conservative, and I am Not. I've met a couple of cool women my age through work, but most women I meet here married young and have kids whose lives they're very involved with, and kids aren't my thing. It's been a bit of a culture shock for me. I am also not white and moving from diverse New Duckburg to the mostly-white Corn City has been strange for me.
For something to do and as a way to meet people, I signed up for a women's programming course through meetup.com. The instructor of the class, Lucy [37F] was awesome and funny. She doesn't have kids, we have tons of the same interests, we had mutual friends/acquaintances on Facebook, and her parents are from the country right next to where my parents are from. We would get coffee or dinner after class every week and by the end of class had exchanged numbers to hang out.
Frank was happy I made a new friend and was excited to meet her, until I mentioned the thing about how our parents are from neighboring countries. He got really serious and said, "Wait, Lucy Fong?" and told me a doozy of a story.
Frank's side of the story: When he was in grad school (age 23ish), he inherited his grandma's 6 year old pomeranian, Trinket, when his grandma went into nursing care. This dog was the most perfect and wonderful and healthy dog who ever lived. When Frank had a chance to go to South America for something school related for 3 weeks, he trusted Lucy to watch Trinket. Lucy, a selfish horrible person, put Trinket in a shady boarding situation instead of watching her, and she was killed. Lucy was unapologetic and tried to stick him with the bill. Ask Caroline (mutual mom friend, 38F), she knows what happened.
Caroline's story: Frank asked around for weeks to try to get someone to watch Trinket, but no one who knew him would do it because Trinket was a nightmare who ****** and **** everywhere, barked constantly, chewed up everything, etc. She had been 'trained' by a senile old woman and then passed on to a busy grad school student who had never had a dog before. Frank finally got his new friend Lucy to watch Trinket, because Lucy had not yet 'experienced' Trinket. Lucy, a 21 year old who lived with roommates, bit off more than she could chew and within a week her roommates said, 'This monster has to go.' Lucy tried to get mutual friends to take her, but of course they all said no because Trinket was a nightmare. She found a reputable boarder, a vet's office, and brought Trinket in at her own expense. Since Frank was unreachable and the vet whose name he left had no record of ever seeing Trinket, Lucy agreed to let the new vet to vaccinate Trinket for rabies, a condition of boarding dogs there. Trinket then had a very extremely rare reaction to the vaccine and passed away a few days later. Lucy felt terrible and borrowed money from her parents to pay the boarding costs. The costs Frank was 'stuck with' were private cremation costs for Trinket to get her ashes.
I haven't talked to Lucy about this yet, but I assume the real story is somewhere between these two accounts, and that this is a case of two 21-23 year olds being tragically unprepared to care for this dog, and that what happened to Trinket was just a freak accident. I also feel bad saying this, but it was pretty obvious to me that Frank's account of what happened is a littttttttttttle bit rosy toward himself/Trinket. Also, we have two dogs together, and I am responsible for 90% of their care while Frank mostly just plays with them and does 'fun' stuff, so I can totally imagine him thinking he was a great dog owner with a wonderful bond with Trinket when the reality might have been different.
I'm not sure what to do now. I really clicked with Lucy in an 'instant best friends' way, and having a close friend here would make life in conservative Corn City a lot more bearable. Of course, I want to support my husband and respect his wishes, and I respect that he loved Trinket and found the experience to be traumatic. Is there any way at this point that I can help him let go of this decade+ old baggage? Is it worth it for me to not 'have his back' here? I think it's most likely that this was just a mistake and that his negligence is a little more to 'blame' here than Lucy, but this might not be a battle worth fighting. I don't know how to proceed.

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TL;DR: My husband's dog died in my new friend's care 15 years ago. My husband is sure that this is her fault, but it sounds like it was more his fault than anything, but probably no one's fault. Can I still be friends with this woman? What can I tell my husband to make him see this more rationally?


Source.

Boy, some of these are beginning to seem like an episode of Judge Judy

Well actually the dog should have already been vaccinated, but i don't think it was the friends right to get that done without the owners acknowledgment of it happening. As far as the friendship goes, i think your husband will settle down and forgive her in time.