Can I claim my daugter on my taxes if she is still attending college, and 26 yrs old?

No - to qualify as a dependent the child must meet the age test, which is that she must be under the age of 24 if a full-time student, or under the age of 19 if not, or be permamently and totally disabled.

Hold on there, guys!

If she has no income or income that is LESS than $3,400 annually, then the parent CAN claim her as a dependent if he/she proviodes over half of her support.

You can claim a dependent under Qualifying child or a Qualifying Relative. Your daughter may still be elligible under Qualifying Relative.
AtlantaTaxExpert has given requirements for Qualifying Relative.

Agreed.