I'll take any chance I can get to use this gif.

I've been with my colourist for almost a year and a half now, and she's awesome. She moved further out of the city earlier this fall and quit at the salon where I got her services. She's over the idea of 'careers', she'd rather do whatever makes her happy. While she's doing whatever it is she does, she's also visiting certain clients at home. I am one of those lucky few. Since she does this under the table and doesn't have to give the bulk of the fee to her salon, she gives me a discount. I'm paying less for more service. But now that she's getting like 90% of the cash I give her... What do I do about tipping? Her cost is her time + gas + hair supplies, which she gets at a discount as professionals do. Last time I saw her was the first time she came over and I tipped her just under 20%. Should I just keep doing this? Or do I adjust for her sudden loss of overhead cost?