Will a home Root Touch Up really ruin a hairdressers work?

[TrudyTrudy]

My ever multiplying grey hair is almost making me bankrupt. Having confessed to my hairdresser that I was finding it very, very difficult to visit every 4 weeks to get my roots re-done I enquired whether I could use a Root Touch Up from the chemist and visit the salon every 6 weeks instead. She told me that I shouldnt use any home applied Root Touch Up at all as it would seriously interfere with my salon roots being done and alter my highlights (effectively ruining everthing) which would in turn cost me more money in the long run to recity the damage.
Now I now dont know what to do. I have read reviews and everyone says they work great in between visits to the salon. Do you think she is just trying to scare me? I still intend to visit the salon but just simply cant afford it every 4 weeks.

[Sachs]

Trudy,
it might be that you would be doing your roots to often if you were to get them done at four & six week intervals. Think it needs to be monthly at least so not to damage your hair?

[tamborine]

Whole base color with veil hilites cost £70 every 6w approx. That's £11.6pw - a luxury I wanna afford!

[spudqueen]

I too have rapidly greying hair, but I only get my roots done every six weeks, are you sure you need to go every four weeks?