For lack of a better spell

[Nanny7761]

I have a player who is playing a multiclassed Witch 4/Rouge 2. She wants to prestige as an Arcane Trickster. She meets all the prerequisites except one, the ability to cast Mage Hand. Mage Hand is not on the witch's spell list, but the description only says the "ability." Could this ability come from scrolls or other magic items and count? Or could I have the player create a spell that duplicates the effects and teach it to her familiar? I'd really like to make this work for the player.

[I Hate Nickelback]

This is a simple question (you're the DM, do what you can to make your player happy), but without Mage hand, AT wont be good. Talk to the player to see if this is what she wants. Maybe let them retrain the witch levels into wizard.

[Morgen]

Something like a scroll or wand usually isn't enough of a justification for a requirement like that.

If their second level rogue talent was Minor Magic for Mage Hand that would certainly qualify for Arcane Trickster. That would be easy and painless.

[Talinari]

How about http://www.d20pfsrd.com/traits/magic-traits/two-world-magic?

[pad300]

let the player use the spell research rules to research Mage Hand. If Baba Yaga can have all sorcerer/wizard spells as well as a variety of divine spells, "Baba Yaga knows all witch spells, as well as all sorcerer/wizard spells. Baba Yaga also has knowledge of many other spells that she has researched. Many of these are arcane versions of divine spells."

I will note that the multiclass is not particularly optimal, as the Arcane Trickster levels will not advance her hexes...

[Adamantine Dragon]

Easiest answer is to just wave the pre-requisite since it is mechanically meaningless anyway.

If you want to maintain rules consistency, spell research exists in the game. My spellcasters are constantly researching spells.