My mum 85 yrs has a large blister on her shin. What should I do?

My dad had a big blister on his ankle. My daughter tried home remedy and I and my mom thought he just needed a surgeon to take a biopsy to see what it was. It turned out to be cancer! I was surprised! The doctor removed the chunk of flesh, which isn’t much flesh, from under the inner ankle. Dad was gardening wearing rubber boots. It was summer and very hot and it stayed wet in the boot from perspiration.

So show the blister to the doctor.

What other symptoms does your mum have? Where do you think the blister came from?
Did she burn herself?
Is she malnourished?
Is her leg red or swollen?
Is she in pain?
Did something rub against her leg to cause it to blister like friction from boots or coarse socks or leg braces?
Does she have a fever?
How large is it?
Give more information please.