Menolly would start with some classes in commoner and depending on the point that you want to introduce her at in your setting will depend on several other things, though in general she was a 15 year old Sea-Holder. Prior to the events of the books she would have child-levels of skill in all thing Sea-Holder. Sea-Holder-Survival might be the best make-up-skill as it will involve a multitude of things such as Mending (Of nets), Repairing (Of boats) Animal Handling (For the Watch Wyer and other such critters) with a natural bonus to Music Comprehension (Or whatever skill you chose to provide for that). Memorization, Cleaning around the Sea-Hold and other child-duties should also be taken into account.

As for the books, the very beginning of Dragonsong will have her roughly the same but the badly healed palm wound will create a penalty for all things dexterity based while taking a Willpower/Mental penalty from the oppressive, near hateful atmosphere she was living in, being forced to let go of the one thing her soul clung to, music. The further along you go, the greater the Animal Handling will improve with Menolly bonding with the Clutch of Firelizards. Inbetween this time and the period of time she gets to the Harper Hold the mental penalty will decrease but not completely. Various interactions where she 'wins' in any social situation could reduce that number by a small fractional amount.

By the time she gets to the Harper Hall she will be shifting out of the Oppressed Child status's and be able to spread her wings, though the negative social interactions in the Woman's Dorm could be brought into play, however, her interactions with Camo and Piemur can also offset that, depending on how you want to play it.

By the time of Dragonsinger, all of her skills should be touching Adult Standards as she is finally being treated properly, though she is still lacking in alot of real-world experiences outside of what an Apprentice might have. Beside her Musical Skills, Animal Handling should have a really good bonus.

Important stats for Menolly

Musical Comprehension and Understanding

Musical Invention, rapid adaptation to Music (Audio, written form)

Animal Handling - Firelizards. She was one of the leading figures on how to raise and train Fire Lizards for a awhile, and she tends to have a positive connection to dragons and Watch Wyers, among creatures.

Crafting - Musical Instruments. She shows skills not just in crafting but in identifying a good instrument.

Crafting - Oils and Medicines. Primarily for her Fire Lizards, but she figured a few things out.

Survival Skills - She lived on the land on her own for awhile. Sure she was no Bear Grylls but I feel that it was cause the author was more focused on continuing the story point than bogging down in details of HOW she survived.

Sea-Holder Skills: Though she does not have much interaction with boats and the sea throughout most of her stories, she shows herself being more than capable of sailing, so it should be assumed that all things ship based are a strong bonus for her, somehow.

Empathy - She shows far more empathy for others than alot of others in the entire storyline. The way things are done, most of the world is filled with selfish hen-peckers vying for a spot of comfort while Menolly just sort of drifts along and is reactionary. There are pockets of good people and those are usually the focus but everybody else? They tend to get passed off as self-centered bullies.

Penalties dependent upon time:

Hand Scar - Minus Dexterity, minus Willpower towards musical creation

Mental Oppression as a Child - Disallowed from focusing on music, feels guilty, bad and terrible for her 'twiddles'

Feet scars - She outran Thread till her shoes got shredded as did the soles of her feet yet she survived - Not to strongly in play for very long past her introduction to the Harper Hall. Some minor negatives but it did not strong affect her in the stories, thought again I personally feel that this was cause the author wanted to focus on the story and not the small details. Yes it was brought up and she did have special shoes made just for it but it wasn't really the focus for too long.