Hi Tantastic
Our first recommendation would be to talk through with your client/friend, the challenges you are facing with their hair colour. There are unfortunately some hair colours which can be trickier than others to match, and being open and honest with your client should be your first priority.
Secondly, if the main problem is that the tone is slightly too golden, purple shampoo may correct this, but adding any kind of treatment to the hair extensions can affect the quality, and this is especially true between different brands, what may work for one supplier or colour may not apply to another.
If you were to tone them before hand, they would become non returnable to the supplier, and you may not achieve the colour you are after, which is why the first point is so important, that your client is completely on board with the situation. She may be happy to take the risk with a slightly off colour match and be happy to apply the purple shampoo herself to achieve the desired match, especially if it is only slightly out in terms of the colour.
Without seeing the clients hair it is very different to advise, however when it comes to blondes, often if the colour is a close match, is does blend better than expected unlike brunettes where a near on exact match is essential.
In regards to the highlights, again, without seeing the client in person it is hard to say, however one word of advise would be to ensure you do not place the colours in a uniform order, ie. one after the other, you need to mix up the pattern to ensure it looks natural and not stripy.
If her highlights are very thin, you could either use thinner strands in that one colour, i.e. 0.5g, or if you are using prebonded nail tips, cut the tips in half so that you have a thinner strand of the colour.
Hope this is helpful to you.
