My mom has HORRIBLE taste...?

Her taste in clothes, decorations, color coordination... I mean, she wears AVON makeup for crying out loud!! And well, I am not the type of person who will tell you what you are wearing looks fine if it doesn't, like I will tell you my honest opinion, well, honestly!! The thing is, my mom gets really sad whenever I "criticize" her in like, for example, fashion... and I always end up feeling guilty for making her feel that way. Like, just about an hour ago, she showed me these shoes she bought from a catalogue or something like that and she was really excited for them, but when I saw them I was like O____O And I immediately sensed that I hurt her feelings... I mean, I don't mean to do it, but it just comes to me naturally... I guess my question is, should I try to help my mom develop a better taste in... everything, or should I try to stop being so critical of her... and if the latter, how should I go about changing my ways, like, should I just fake it and tell her her tacky green polka-dot dress looks good, or should I just NOT say anything at all??