*However*, if you want Tali to be involved with it (the main missions), you should wait until you're at least done the Rannoch mission-arc and Tali permanently joins your party. It is available right after the Citadel (mid-game) mission. You can certainly install Citadel DLC (or any other DLC) during mid-game. A point of caution (kinda spoilery but important to know) - if you romance her in ME2 but drop her/romance another in ME3, unless you do a specific workaround, she will *die* in ME3.
She can be part of the final big party and goodbye She can join you in the Armax Arsenal Arena (She is NOT involved with the 4-mission main story arc) Goodbye conversation, Extended Cut DLC content
