I'm a criminal lawyer and can try to assist.
First off, I hope the police use their discretion and decide to not lay a criminal charge; perhaps just a verbal warning, given the circumstances of what you say happened.
IF the police do decide to lay a criminal charge, the two potential charges would be (1) Assault or (2) Assault Causing Bodily Harm (depending on whether the security guard suffered any injuries as a result of the bite).
If the matter proceeds to court, there are a number of ways in which your daughter can approach the case in order to put herself in the best possible standing to walk away without a record. Hiring a criminal lawyer would be the first step, as there are potential legal issues involved (specifically the idea of Self Defence) which might be used as leverage with the Crown Attorney to get the charge withdrawn. Self Defence is a complete defence to a criminal charge, and involves the idea that we are allowed to use physical contact to ward off another person if that person has initiated physical contact with us, provided that the responding force we use is (a) reasonable in the circumstances and (b) was used for the sole purpose of being free of the actual or threatened physical contact.
If your daughter is charged with this type of offence, you say it would be an out of character incident. Your daughter could gather supporting documents after being charged to provide to her lawyer in order to establish, by way of objective documents, that this was an out of character incident. Documents of this nature can include: character reference letters (which specifically highlight that she is known to be a non-violent person); letters confirming employment; letters confirming her involvement in the community, etc. Any supporting material your daughter comes up with should be provided to her lawyer - NOT the police and NOT the Crown Attorney. A lawyer would need to ensure that there is nothing in these documents that could "hurt" the defence strategy (for example, a strategy to convince the Crown Attorney to withdraw the charge).
I hope this helps. If it has, please consider providing a positive rating.