Two females cannot "have sex." This is semantic bullshit introduced by the gay community to try to "normalize" their sexual practices.
You might remember in the ancient past we had a President who truthfully told America that he did not "have sexual intercourse" with Monica Lewinsky. Receiving (or giving) a blowjob is not "having sex." Same for handjob, stink-finger, fudgepacking, titty-*******, and any other non-reproductive activity which artificially stimulates a sexual response from the reproductive organs. They are all forms of masturbation, nothing more. And just because there are two people involved, that doesn't elevate it from mastubation to "having sex."
Sex is a reproductive act. Except for those (liberals/progressives) who insist that words mean whatever the **** they want them to mean at any given moment.
To the case at hand...there is a chasm of maturity difference between a normal 18-year-old and a normal 14-year-old. There is a reasonable presumption in the law that an adult can exert undue influence on a minor to induce the minor to engage in activity that the minor would not engage in, absent the undue influence. And a minor cannot consent to have her parts played with by an ADULT - she lacks the legal capacity to do so.
Thus, the 18-year-old has done something for which some legal sanction is probably warranted. But it ain't "rape," by any rational definition of the term, and the punishments called for in cases of rape and statutory rape would be grotesque overkill in this case.
Tell her not to do it again and forget about it.
Is that an option?