My mom is very sedentary and sits for about 10hrs a day. She has Chronic Inflammatory Demylinating Polyneropathy (CIDP). She is a bit overweight. She has a huge abdominal wall hernia (from busted abdominal stitches after a huge surgery and an immediate repair was not possible), a colostomy and she is somewhat incontinent and therefore wears disposable underwear. I got her an egg gel cushion to sit on. This is on a cushy couch not a hard surface or wheelchair seat. She has these circular patches on her butt cheek the best way to describe how they look is like when you have a blister and you pop it or however the top layer of skin is removed what's left is the circle of dark pinkish purple skin with the sort of dry skin ring around it. These areas aren't moist or oozy they seem pretty dry and don't appear very sore looking but they can feel sore to her. There are different sizes some are about 2" diameter and some are smaller. Some are a light colored pinky purple and some are more dark purple. I thought they may be pressure sores (but not ulcers) so have been putting hydrocolloid bandages on them (doctor said that's the right treatment based on the description I gave but she has not seen them herself) However, since these are on her butt cheek and upper thigh it is very difficult to get the bandages to stay on due to being rubbed every time the underwear are pulled up /down and the shear fact of the area being sat on and then scooting motion when getting into bed. The bandage edges roll up even when I put surgical tape on to hold them down. It's a mess and frustrating and I'm trying to find a solution if one exists. I'm also not 100% sure what the spots are or if I'm treating them correctly. If anyone has seen skin irritations like what I've described please respond so we can discuss.
There are many things that can cause petechiae, so you may want to "Google" to see if anything may apply to your mom.
My husband who developed sepsis and septic shock after almost dying from aspiration pneumonia, developed petechiae all over his legs and eventually his hands as well. I didn't have to do anything to "treat" it for him as he was under hospice care and it never bothered him.
I hope you get a proper diagnosis soon, so she can be treated accordingly.
As for bandaging, depending on exactly where the wounds are located, you may have more luck with large gauge pads that you use her underwear to hold in place instead of tape.
https://facingdisability.com/preventing-bedsores-and-pressure-ulcers/signs-and-symptoms-of-bedsores-stage-by-stage?https://facingdisability.com&gclid=EAIaIQobChMI2OHfkPyK8wIVz2tvBB2_9Qt1EAAYASAAEgKBLfD_BwE
I don't have a lot of experience in this area, but they sure sound like bedsores. Which can get dangerous very quickly.
The fact that there are several would seem to indicate that her seatng is inappropriate. The pressure needs to be gotten off her butt and thighs. A recliner might be better, and a specialized cushion like a Roho or similar might be advised, but I think above all you need to get a would care specialist involved.
Using surgical tape on her fragile skin seems like a bad idea. Please get her seen asap.