Does Diana no longer human +2 each time a spell is played?

Yes, Diana, No Longer Human gains +2 Might each time you play a spell.

According to her card text, Diana has the ability: "When you play a spell, give me +2 [S] this turn."

Here is the breakdown of how this interaction works based on the game rules:

1. Triggering: When you play a spell, the ability triggers. Because it is a triggered ability, it is placed on the chain (Rule 355.10.c).
2. Resolution: Once the spell resolves (or if the ability is placed on the chain independently), the effect resolves, and Diana receives the +2 Might bonus until the end of the turn.
3. Stacking: Since the bonus is granted "this turn," multiple instances of this ability will stack. If you play three spells in a single turn, Diana will receive +6 Might total for that turn.

Important Nuances:

• "Play" means resolution: As established in the game rules (and supported by FAQ #2190 regarding similar triggers), a spell counts as "played" when it resolves on the chain. If a spell is countered, it does not resolve, and therefore it does not count as being played for the purpose of triggering Diana's ability.
• Repeat: If you use the Repeat keyword on a spell, it counts as playing the spell only once (as noted in the Patch Notes - 2025-05-12). Consequently, Diana's ability would only trigger once for that spell, even if the effect is executed twice.
• Timing: Because this is a triggered ability, it uses the chain and can be responded to by other players before it resolves.

Note: I could not fully verify this ruling against the retrieved rules.