Q. Does she owe any SS/Medicare/Federal/State taxes on $2500 income in 2020?
A. No, as discussed above. Also, as discussed above, there is a weird exception. She owes SS/Medicare if you (the parent with the DCFSA) are divorced (and not remarried) or widowed,
Your description of your situation brings up a question you didn't ask. Why isn't your mother your dependent? She lives with you and has no income.
A person, who can be your dependent (whether they are actually your dependent or not) can not be a qualifying care provider for purposes of using DCB/DCFSA or claiming a dependent care credit. From the instructions for form 2441:
"The person who provided the care wasn't your
spouse, the parent of your qualifying child, or a person
whom you can claim as a dependent."
