Back up bridesmaid

Please post anonymously on Facebook : so 7weeks before the wedding one of my bridesmaids has pulled out of the wedding - I’ve been really upset and it’s been pretty traumatic. At the time of choosing bridesmaids I had quite a few friends to choose from but didn’t want more than 3 bridesmaids as HTB had 3 groomsmen, so I left a few friends out. My HTB says now that she is out I should ask one of the girls not initially picked to be a bridesmaid but I’m worried it’s too close to the wedding and I don’t want her to feel like second best. I’m a bit lost with what to do as still dealing with the hurt of my initial bridesmaid not coming and ending our friendship and I don’t want to make the wrong decision and upset another friend accidentally.