It's definitely possible to have a low sed rate and have very active Crohn's. Some people have completely normal inflammatory markers while having active disease - my daughter did, when she was diagnosed. ESR was very low - like 2 or 4 or something. But scopes still showed ulcers and inflammation.
If she's still bleeding, her IBD is definitely not in remission, no matter how low her Sed rate is.
My daughter had a similar situation - her Ferritin levels were found to be very low. This was before she was diagnosed with Crohn's. We saw two hematologists and both said she must have bled at some point since her iron stores (Ferritin) were so low, though she had never seen blood in her stool - no red, nothing black or tarry.
We tried oral iron supplements but they didn't increase her iron levels, so moved on to infusions. Those helped her - got her iron levels up.
About a year after she needed iron infusions, she was diagnosed with Crohn's, so her GI thought that she must have bled at some point without knowing it/seeing it. Her GI said if we kept the Crohn's under control, then she shouldn't need any more iron infusions. She was put on Remicade and MTX and her Crohn's got better. And she hasn't needed iron supplements since then.
So I'd definitely want a second opinion with another GI to figure out whether she has active inflammation in her gut or not. You could also see a hematologist and rule out other stuff, but my guess is that if she's bleeding, it's like the Crohn's.