You mention it was a SanDisk Extreme card. That card normally comes with a free download of RescuePRO recovery software.
Try the software. If it can see the card...that is, recognize the card as there, then you should be able to recover the files.
However, you also said that you saved new pictures to the card. There is a very good chance that those new pictures may have overwritten the ones you were wanting to recover.
If the software does not find the files, consider professional recovery services.