Note that if you are not the biological father, you can't claim the child.  If your GF has more than $4,050 of taxable income in 2017, then you can't claim her. If the GF is older than you, then you can't claim her.
First, your GF needs to file an amended tax return. Since amended tax returns can not be e-filed (the IRS says so) she will have to mail it to the IRS. Amended returns take 12-16 weeks to process.
Next, since your GF already e-filed and her e-filed return was accepted, that means the dependent she claimed has been marked as "claimed" in the IRS computers. Her filing an amended return will not change that. Therefore you would not be able to e-file your 2017 tax return if you claim either or both as your dependent. You would have no choice but to print, sign and mail it to the IRS.

You MUST wait for the original returns to be accepted or rejected before doing anything. Then you will efile or mail your return as soon as your girlfriend's Amendment is completed with the IRS.

If the returns are rejected you can make the needed changes then resubmit them.  

If the returns are accepted you MUST wait until they have been fully processed and you have either received the original refund or paid the original balance due before amending them.  

Follow these instructions to amend:

1. Sign in to TurboTax and make sure you've selected Tax Home on the left side of your screen.

• If you don't see this, click or tap the 3 white lines in the upper-left corner to expand the menu.

Under Your tax returns & documents, select Amend (change) 2017 return.

Carefully follow the onscreen instructions and don't worry if your refund changes to $0. This is normal on amended returns.

When finished, we'll give you instructions for printing and mailing your amended return, as amendments cannot be e-filed.

3 weeks after mailing your amended return, you can start tracking it at the IRS Where's My Amended Return? tracking tool. Please allow at least 16 weeks for the IRS to process your amended return.

Processing times for amended state returns vary from state to state. If it's been more than 12 weeks since you mailed your amended state return, and you haven't heard anything, we suggest you contact your state tax agency.

You can check the status of your Form 1040X, Amended U.S. Individual Income Tax Return, using the Where's My Amended Return? online tool or by calling the toll-free telephone number 866-464-2050 three weeks after you file your amended return.

 

I filed a return and ended up pushing the wrong button on can someone els clam u as a dependent and I didn’t realize that untill I already e filed it so I waited to get my return and the did a  Amendment about 6 months ago and I haven’t heard anything back about no money no nothing and every time I check on the we’re my amended return it says it’s not available at this time well it’s been way past the 16 weeks what should I do because it say I could slow down the process by sending off another Form but I’m wondering if they even have it or if it got lost in the mail or what so please tell me what you think I should do me and my family could use that money right now I lost out on about 3 grand :(

In normal times it takes up to 16 weeks or more to process an Amended 1040X return. But these are not normal times. They just started opening the mail in June that's been stacking up. Back in March the IRS closed their processing centers and stopped processing mailed tax returns. An IRS spokesperson recently said that they have about 11 million pieces of unopened mail. The IRS says.."We’re experiencing delays in processing paper tax returns due to limited staffing. If you already filed a paper return, we will process it in the order we received it." So you have to keep waiting.

 

See this IRS page for the latest information

https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue