Senior dog with arthritis, when is it time?

Just like the title says, I have a senior dog who has arthritis, and I just don’t know how long I should let her go through this. She’s a rescue so I don’t know exactly how old she is, but we guess around 12-14

We’ve tried metacam, it didn’t do anything. We have her on a low dose gabapentin but that also doesn’t seem to be doing anything. I know there’s a new monthly shot that’s on the market, but we can’t afford it. She’s already on extremely expensive food for pancreatic care, and we have a new baby so I’m off work.

I feel so bad for her, I can tell she is in pain every day. It used to be just her one front leg, but I can see it in both her back legs now.

She’s not the greatest eater. She’s lost a good amount of her sight and hearing, she needs to wear diapers inside because she can ‘leak’ sometimes. But she still gets excited when we come home and she jumps around, she’s excited to go outside even though she doesn’t want to be out there very long.

She’s not sick so feel like it’s not a very obvious time to let her go, so I’m not sure what to do. She’s my first dog so I don’t want to let her go, but I don’t like seeing her struggle with walking, I don’t know if that’s even something to euthanize her for though. When do I know it’s time?