Op you sound like you're going to set out on your first foray into having employees really really badly. Sorry but you need to step back.
Pay her a fair market rate for the role,offer it to the best candidate/her if you want to, and let her decide.
You shouldn't be trying to wrap your head around someone's finances, it's a business, not a charity, and it's ridiculous to try and tailor your future wage increase offer based on what you guess is her financial position.
Put it this way - I've never had a job or an employee whose wages reflected whether they had kids or not, or were a breadwinner or not... Just a reasonable market rate reflective of the skill, locale, etc required.
Make sure you issue a basic contract setting out employment terms such as notice periods, holiday entitlement and contracted hours, and provide wage slips etc.
(As a tip, I work with a "single parent" who is actually a co owner in a soft play centre after having a very very good inheritance split between her and her siblings.. her actual part time job is because she enjoys it so she continued it, but went from full-time to part time when her proper income, the soft play opened. You don't know anyone's finances by guessing.)