AIBU to consider putting our elderly dog to sleep?

[Ghasha]

My dog is almost 13 years old, she's been a great family dog and we all love her (especially the kids)
Last year or so she's really changed, suddenly seems very old, has a lot of lumps and bumps, doesn't enjoy walks as much as she used to - is very slow. She often walks around the house aimlessly, she'll stare at walls and cry or sit in the middle of the garden and cry. She seems ravenous and will cry for more food when she's already eaten, she's looking thin despite this. She's also gone to the toilet in the house a few times overnight (something she never does) Her eyes also look like she could be losing her sight. Up until recently I've thought she's just getting old but seems ok in her self most of the time, will still cuddle up with the kids etc.
Last week she randomly attacked our cat (who she's lived with since she was a puppy) he was ok luckily but we were all shook up, can't see a reason for it - he wasn't anywhere near her or her food or anything like that.
Tonight she randomly snapped at my hand when I bent down to pick a tea towel off the floor. It really shocked me.

Up until now I've been reluctant to see a vet because I imagine they'll suggest tests/scans or the like, we live hand to mouth as it is. I'm slightly concerned her behaviour is indicative of cognitive decline.

Part of me thinks if she continues to decline it might be the kinder (and safer) thing to have her put down.

What would you do?

It's hard @Ghasha to know when to call it with an elderly pet. It sounds as though it's time if only because of the snappiness.
My girl is a similar age. She has cataracts, gets stiff when it's rainy (she has arthritis and associated meds), but is a happy wee monkey. All the same, I'm vigilant for a downturn in her wellbeing.
I'd be taking your wee doggy to see the vet and get their advice.

If an animal is not well you take them to the vet.

There are vets who offer payment plans, and PDSA as already mentioned. She cannot take herself to the vet, you are responsible for her wellbeing. It is cruel to deny her the medical treatment she needs. If you cannot afford to keep an animal (and that includes taking care of their health) you have to find a way or you shouldn't have that responsibility.

It could be diabetes, dementia, or a pain problem. It could be something you and I have never heard of. But she needs medical attention and you are the one in charge of that. Do not put it off any longer, the poor thing.

When did you last take her to a vet? Has she ever been insured? Take her to get seen and decide based on outcome. 13 is a great age for a dog to make it to

Our beloved dog slowed right down, would stand and stare, go outside and promptly turn back round. Started eating less and less and finally didn’t want to drink. We believe she had decided that at fourteen she’d had enough. We did what we and our lovely vet thought was the kindest thing and let her go. That was just as the heatwave hit and we miss her terribly but know she had the best life and that it was our final act of love towards her.
Do think of your poor dog it sounds much like dementia hard as it is we have to put them first b

It sounds miserable and upsetting for you and for her. IIWY I would definitely be considering bringing this to a humane end rather than prolonging things to...well, what!?