Advice needed: BFF to be in-home nanny...

My best friend is going to be my in-home nanny once I go back to work. (I am currently 15 days PP and going back to work in another few weeks) ...We haven't discussed pay yet - I think both of us feel awkward bringing it up to arrange details - though we both know she will be getting compensated in some way. Looking for advice for what is reasonable pay?? (Does anyone else here pay for in-home care?) Here are the specifics which need to be taken into account:
1) She will be coming to my home
2) She will be driving close to an hour each way - 3 days per week, M, W, F. (She claims she doesn't mind, is "thrilled to get out of the house.")
3) She has her 5 month old that she will be bringing. 
4) Can help herself to food in my fridge for her and children. 
5) Can use my diapering supplies
6) She will be getting ***paid under the table***
7) She is not looking to be paid at a day-care rate or I would just be opting for that...
Huge perks for me that I need to take into consideration:
1) I trust her 100% with my baby. She has tons of experience and has been my BFF for over 25 years. 
2) She comes to me - my own home and environment baby is comfortable in. 
3) socialization with his (hopefully) future best friend :-) - my friends 5 month old son. 
*** I want to offer her something that works for both of us. Something that is less money than day care (as money is tight) but also FAIR for her and not insulting. (But something reasonable I can afford for long-term arrangement)