'My sister-in-law is crowdfunding for her sick cat, and I refuse to donate a cent.'

Despite trying to, I just don’t get along with my sister-in-law, Lisa.

Aside from the fact that we clash on everything from fashion to TV shows, our history has been marred with incessant bitchiness and a refusal on her part to pay me back the hundreds of dollars I’ve lent her over the years.

I understand that she’s the wife of my brother, and they’re happy, but I can’t let go of the things she’s done.

This brings me to my biggest annoyance – her cat.

You see, my brother was against Lisa buying a pet when she announced she wanted one last year. They’ve been financially struggling for the few years they’ve been together (mostly because of her terrible spending habits), and Michael knew the added expense of a cat could be an unnecessary strain.

Despite his constant protests, Lisa came home one day with an expensive Persian pedigree, and their lives haven't been the same since.

Sadly, the poor cat has a genetic disorder that means in her short life she's had two huge surgeries, costing $3000 a pop.

Obviously, I feel horrible for the cat, but I can't help but resent Lisa for bringing this additional financial pressure onto my family members, particularly considering that so far, my parents have paid for both surgeries, and Lisa hasn't had to pay a cent.

My brother does what he can to chip in, but a work injury has left him without a trade job for the better part of a year.

I'm furious that Lisa makes foolish financial decisions and that she continually takes advantage of my parents' generosity. Within four months, Mum and Dad have dished out nearly $7000 for vet costs, and have told me they're now starting to stress about money, too.

One week ago, while busily scrolling away online, I landed on a solemn Facebook status from Lisa, explaining that an emergency third surgery is now needed to save the cat's life. Alongside a tearful photo at the vet, was a heartfelt plea for friends and family to donate $2500 for the surgery.

LISTEN: "Pets are not your kids." (Post continues...)

What's worse is the day before, Lisa was posting photos of an expensive weekend away with work friends, a vacation that probably cost upwards of $1000.

I sat staring at my iPad for the better part of a minute.

"You've got to be kidding me," I hissed while dialling Mum's number. After all, this is Lisa's cat, and when you agree to be a carer of an animal, you should be responsible for it... right?

"You're not donating, are you? This is getting ridiculous - she has a job, she needs to start paying for this cat herself! I'm not giving her a cent. You can't just crowdfund your financial problems."

"I felt like I had to," Mum told me sadly. "We gave another $300, just to keep the peace. I spoke to Lisa and got the strong impression she'd be really disappointed if we didn't all pitch in something."

Sometimes I wish my mother had a slightly colder heart.

"I feel sorry for that poor cat... but I refuse to perpetuate this bullshit."

And so begun the silent family war that's now threatening our summer family reunion, which will be the first time I've seen Lisa in months.

While my sister gave another $100, I am defiant that, on principle alone, I will not give anything, because donating money would only validate Lisa's reckless and selfish behaviour.

On the flipside, Mum and my sister say that $100 is a low price to pay for a peaceful and cheery reunion.

I've started to doubt my hard-line approach, and now I don't know what the right thing to do is.

What would you do in my situation?