Installing mini blinds inside mount and hitting metal

I am helping my daughter who is replacing all the old vertical blinds in her bedroom windows. they bought this house which is maybe 20 yrs old. 2 of the upstairs bedrooms have arched windows. these are vinyl windows. She put a curtain rod up but had a very difficult time because the drill bit hit metal just under the wall board, about 1-2 " beyond the window. (not inside mount) She wants to install 1" blinds inside mount. I am guessing the metal will there too. Can we use a hammer drill w/ metal bit and proceed as usual to secure the brackets?

So the blinds will hang about 20 inches below the top of the arch. about 5 in. depth of window. we will then hang a rod above the arch for a curtain that goes the length of the window to the sill.