very long hair color breaking disaster- Pls help!

I have very long naturally wavy, porous dark blonde hair that I had used Loreal Castings on to cover gray that lifted my color just a little. This was fine except I had a line of new growth that I wanted to get rid of. I went to a professional and asked for my regular hair color back maybe w/ some highlights, but told him I did not want to damage my hair, because of it's length and how fragile it is. He used a demi-permanent color all over my hair, and foiled some highlights in the front. Then I was shampooed VIGOROUSLY for about 10 mintes. I now have BROKEN hairs all over the place! My hair looks terrible, and the texture is rough and straw like, no body or shine. There are more broken hairs I believe than long hairs (and this has only been 10 days). I have used deep reconstructors, moisturizers, olive oil, and frizz products.. nothing is making it look any better.

Someone suggest Henna would seal and condition my hair. Can anyone give me feedback on this? I will probably have to continue coloring the new growth as it grows in a different shade. I read that you can't put any coloring over henna... but read somewhere else that henna comes out in 6 wks or so. If henna coloring itself works well on dark blone hair I think I would prefer to stick with natural coloring at this point. But I do not like red undertones. If not color, would clear henna help the condition of my hair w/out any lasting negative effects?

sorry for the length of this post but thought all info may be pertinent--

thanks in advance for any help, :)
Bree

I have very dark hair and tried to lighten it to blonde and it got very dried out and broken too. Unfortunately the only thing you can do is cut it a little bit at a time as it grows out. Also when you use conditioner, Do your final rinse with cold water because this seals the hair and keeps the conditioner in. I also suggest putting a dime size amount of conditioner in your hands and rubbing it through out your hair after the rinse and then comb and style as usual. This will give your hair extra protection while it is growing out. It works really good for me! I hope this helps!
Elizabeth