That's fascinating, I wonder why that suggestion would be any more dangeous than any other advice. Too bad she didn't just put in a footnote describing why she can't suggest asking for 10% more.
The Worknumber product from ADP (and it's equiv from Paychex) covers a vast range of white collar employees. Perhaps most.
Your new employer has a very good chance of seeing precisely what your current salary is down to the paycheck level going back years to even verify raises and title changes.
Replying with what you require to make to take the job seems like a much safer bet to me.
Might be wise to do before you interview.
You may not remember to opt back in to the "service" a certain number of months before you buy a car, for example. Then you're stuck either paying a higher interest rate because the lender sees you as riskier without a trusted method of verifying income, or you have to do a bunch of paperwork with the seller or finance company may or may not be willing to deal with.
It doesn’t have to be a lie. Between base salary and the value of benefits (and expected value of equity) you have a wide range of where you can answer what you’re paid, what your compensation is, what your “take home” is (what does that even mean if you’re W-2 and 1099?), et cetera.