Could you soak her while you do her shellac mani after her feet and the skin should be soft enough once your done to give a quick foot file, scrub and moisturise?
To be fair I would just say 'omg your poor tootsies, what have you been up to??
They need a good exfoliate and massage,bet they are killing you aren't they? keep it quiet and ill give 'em a quick scrub and rub while your here to Keep you going but you need a proper pedi next time otherwise you're going to end up sooo achy'
Xxx
Do you know what...I'm just going to have my foot spa and all the bubbles going, so when she comes in she'll be too tempted to say no!
And I'll just say to her "oh, I thought we agreed last time that you were going to treat yourself to a luxurious, relaxing pedi"...she won't be able to refuse!