In any situation, you can always approach the table and use whatever conversation starter you would normally use. If there are extra seats at the table (or nearby chairs you can easily drag over), you can sit down while delivering a false time constraint. Sit in such a way that implies that you are about to leave any second. A couple of ways to do this include turning the chair around so it is "backwards" (i.e., you are looking over the back of the chair), and/or, about a minute or two later, standing up from the chair as if you are about to leave, before they say something that "catches your interest" again and entices you to sit back down.
If there are no obvious extra seats, you need to steal hers. Reach your arm out, palm up. Tell her to stand up. Raise your arm directly up to "spin" her (she is doing all of the spinning; you just touch her hand) and while doing this, move behind her and sit on her chair. Tease her for a second that you stole her chair and deliver another false time constraint. You're implying that you're about to leave and that you will give her the chair back. Within a couple of minutes, you will either need to let her sit back down and go get another chair, move her somewhere else where you can both be comfortable, or put her on your lap.
Here are two scenarios you might encounter, along with a solution on how to handle each of them.
Scenario 1: She is sitting at a large table, there is space available, most nearby tables are full, and there is a reason to be sitting down (e.g., a coffee shop).
This is the easiest scenario, but fairly rare. Just walk straight over to the table and say "do you mind if I sit down?" in the same way you would if it was a man at the table. Then, not right away but within the next 20 seconds, begin a conversation. You should use a very low-energy opener in this situation. This is the easiest way to approach this situation, but you can also use the strategies from earlier in this article if you prefer.
Scenario 2: She is sitting at a table either without extra room or where nearby tables are empty. Sit at a table close enough to hers so that you could comfortably have a conversation. Ignore her for the first couple minutes, and then initiate conversation in the same way as in the previous example. Again, this is just a shortcut. If you prefer, you can still use one of the strategies from earlier in this article.
The general rule is, don't keep standing while everyone is seated. This will lower your social value. Take a seat as soon as you can, use a false time constraint, and go from there like you talk to any other group of people.