It takes time to find the right pads for you. She needs to start with the lowest ones and move up, it shouldn't take too long to find the ones most suited to her needs. It sounds like those she is using are not the right strength for her needs.
Although I'm not elderly, over the last ten years or so I've dealt with increasing health problems. A few years ago when an elderly relative suddenly found themselves terminally ill the worst part was learning that their body had changed drastically and they'd never be the same again and though my condition isn't terminal the battle inside is the same. It takes a massively long time to cope with it - I still struggle a lot with it. It wasn't something I understood until it happened to me and I think it's something that is drastically under estimated as an issue, for everyone. With respect it's not really something you can help with. She's dealing with a lot of conditions from what you say and incontience is humiliating and it's something you feel you must be able to fix yourself, there's an element of feeling like you're regressing to being a baby again (I know that sounds stupid but it's how it feels). I don't know if that helps you to understand. I know when I began needing them it would take me forever to purchase them and I've noticed people in the pharmacy which is close to the incontienece pads hanging around looking like they're really embarrassed, it's sad to see.
There is also physio exercises that can help. They don't help me because of the nature of one of my conditions but I've heard they can help slow it down.
I get recurrent UTIs for three reasons, one my bladder doesn't fully empty (I'm aware of the irony of being incontient and not being able to fully empty my bladder), two I react to whatever the crap is that's put in pads to stop them smelling (which can and does cause UTI problems because when you're incontient you use them all the time so the chances of a reaction are much much higher than with sanitary pads) thirdly, it's not always possible to change a pad the moment you need to and that can cause problems.
UTIs mean you need the toilet a lot. One thing that could be tried is a daily antibiotic once she is clear of infection to keep a level of antibiotic fighting the infection. The NHS don't like doing this because of resistence, but I've found I need far less full courses (and I need more than just three days recommended) taking one a day. There are things that can help like avoiding acidic drinks - cranberry juice makes mine worse as do those sachets from the chemist, but you can get cranberry tablets which some people have found helpful. There is also a condition called irritable bladder syndrome which can like irritable bowel syndrome be connected to stress.
It sounds like she's really struggling to cope with the changes which is totally normal, I know I'm words on a screen but you can tell her what she's feeling is very normal. It is upsetting when it feels like your body is refusing to behave (it's not logical but then emotions never are).