I’d go with disgruntled, but not for the reasons you’re thinking of.
First, not knowing your own strength is an issue, for both men and women. But, without training or experience, most combatants have a hard time generating force. Which outright cripples their damage, regardless of gender.
Second, your character isn’t going to be able to surprise their partner, at least not by hitting harder than they’d expect. If they’ve been training in contact sparring (of any kind), they’ll be used to taking hits. And your character isn’t going to be able to best them. They have training and experience on their side, and that will win them the fight.
Third, and this isn’t what you were directly asking about, you don’t train someone in martial arts by having them spar with anyone.
Sparring is something reserved for advanced martial artists because, if you let beginners spar, they’ll just end up seriously hurting each other. I’m not saying it doesn’t happen, but getting caught “sparring” will get you kicked out of most martial arts classes. Usually, you won’t see anyone below black belt, involved in unsupervised sparring.
There are a couple, very specific exceptions, that aren’t technically sparring, but could be mistaken for it:
Some katas require a training partner. It’s not actually sparring, they both have a script they’re following. Usually this is either because the kata contains material that requires another human sized object to throw or because the practitioner is having their skills evaluated. If it’s the latter, then this is probably, strictly, no contact. Meaning, the martial artists never touch one another.
When practicing a specific technique that requires a partner, including throws, blocks, holds, hold counters and joint locks. The issue here is, these techniques really can’t be drilled without a living partner.
When a technique can be drilled by shadowboxing, most of the time, that’s what the instructor will have their class practice. Remember, they’re there to teach their students, not kill them.
As a martial artist advances through the ranks, they will be allowed to participate in supervised sparring. This will be with a master observing their techniques and responses, but it won’t happen before they’ve been trained to have a solid grasp of the basics.
This is a little different with the Military’s eight week training programs. But, again sparring is something that’s only introduced after the basics of hand to hand are established.
There is nothing you can learn from having your ass handed to you by a more experienced fighter, before you know what you’re doing. The same is true for your character.
If your character is a master of one form, and is seeking admission to another school, then you might have the classic evaluation duel. Where the point is to prove that your character has the requisite skill. It’s a little cliche, but at least it makes some sense there.
Extracting that cliche and applying it to a new recruit isn’t something a credible martial arts school would do, unless they’re card carrying Saturday morning cartoon supervillians.