This is really confusing, because you're not giving any details at all. What do you mean she requires your help cuz of the accident? Also, if she's only a week late on rent, why would the landlord want a co-signer? The only reason I can think of is she's habitually late and/or is a couple months behind and he's tired of this. It's also possible you're violating terms of her lease, and if you're staying there, he wants you on it.
All I know is, never co-sign a lease for another adult, and that includes your daughter. If the accident wasn't her fault, she can get an atty and try to get some emergency help from the other person's insurance. If it was her fault, I have no idea what to tell you.