18mo constipation?

My 18mo has been constipated the last few days, she's straining when she poops and only a little nugget comes out. She is doing this multiple times day so she's got a bad rash from all of the wiping. I've tried giving her a liquid stool softener but she won't drink it because of the taste (even when it's mixed with juice). What else can I try to help her?