Ds did this. One tooth got pushed back slightly and it started going grey after a few days. I did take him to the dentist as I was worried but the dentist said it would either continue to get darker as the nerve dies, but it's nothing to worry about; or it would get better.
It's probably about 9 months since the accident now and his tooth seems to have returned to its original place and colour.
So I'd say she doesn't need to see a dentist, but it would do no harm to take her if you wanted to ask them about it.
Dd (2.6) did this on Thursday and ended up with two wonky loose teeth (plus bruised purple gums, swollen lip and bruised nose) I took her to our minor injuries unit who checked her out and advised going to the dentist. The dentist was fab - I thought her teeth were only wonky but he said they were actually knocked loose. He said the same as gingerwhinger - that the teeth are likely to go grey but nothing to worry about, and as kids are so resilient, her teeth wouldn't be loose for long. He said that it might be best to give her soft food for 7 - 10 days as that's how long it would take the teeth to settle. He also said she would probably eat on the 'good' side of her mouth for a few days. Three days in, being a toddler she bashed her mouth again today and her gums started bleeding again and tooth looks even wonkier....