The definition of what kind of interaction constitutes rape is normally defined by statute or by case law, which can vary somewhat from jurisdiction to jurisdiction.
Typically, "penetration" for sexual gratification secured by force would constitute rape, regardless of the gender of the perpetrator.
Typically, "penetration" does not cease to be rape because it is not accomplished with a male penis.
For statistical purposes, the United States Department of Justice defines rape as:
Penetration, no matter how slight, of the vagina or anus with any body
part or object, or oral penetration by a sex organ of another person,
without the consent of the victim.
What you describe sounds like something that would qualify as rape under most jurisdiction's definitions of that crime.
None of the exceptions to the U.S. Department of Justice's definition of rape (e.g. legitimate medical examination or a law enforcement cavity search where one is authorized by law) apply in this case.
Even if a particular jurisdiction didn't classify this as rape (and the vast majority would), most would, at a minimum, classify this as sexual battery (i.e. forcible sexual contact not amounting to rape under the local definition), or simple battery (i.e. forcible contact without permission that is not necessarily sexual).
Of course, even if it meets the legal definition of rape, a prosecutor or law enforcement who is accustomed to thinking of rape as exclusively a male upon female crime could balk at prosecuting the incident as rape, something that can be hard to get them to take seriously and prosecute when acquaintances are involved even in opposite sex couples. Law enforcement and prosecutors have broad discretion regarding which crimes they prosecute and for which charge.
About 1% of people arrested for committing rape are female, and while some of those cases involve materially aiding and abetting a male perpetrator (e.g. by holding down a victim while the male perpetrator engaged in the act), some of those arrests involve the fact pattern that you describe.
In part, the low rate of female arrest for rape arises from the fact that women commit violent acts, in general, at a much lower rate than men. The low rate of female arrest for rape also almost surely involves underreporting of rapes committed by women against women, in part, because women are less likely to conceptualize what they have experienced as rape and, in part, because law enforcement is often insensitive or dismissive of these charges in many places.