Definitely get some experienced help, for safety’s sake.
If she’s that sore look at diet and management, are they contributing to the thrush; sugary feeds will, as will dirty living conditions, metabolic conditions like ppid can too.
Consider what medication you are putting on them, some can really sting and make them sorer if it’s a bad case of thrush, don’t use bleach, even some things sold specifically for thrush are so strong they flinch at them. Don’t scrub/pick too aggressively either.
Try a soak so you don’t have to get in too close, a one off cleantrax is the gold standard as far as I’m concerned, but you may find a 50:50 apple cider vinegar:water mix used twice daily quite effective, or something else gentle in a foot bath.
When you can safely handle the feet use red horse products, they’re gentle and soothing but also highly effective at killing thrush.