No she's still within breed standard and therefore you could still show her - but whether she will be sound enough or good bite is another question. Obviously I wouldn't breed from such a small one - if you are likely to want to breed in the future I would say no.
A lot of people wouldn't buy a small one as some judges will knock a bitch if they are not big enough to breed from - my argument with that is that it doesn't say in the breed standard that they have to be bred from.
She looks quite nice - what's her mouth like? She probably will fill out at bit as she gets older. I have a boy who looks very small but weighs 5lb 3oz - to look at him you would think he would be pushing 4lb
As said above ive seen bitches be dismissed due to being too small. Shes lovely but her face isn't very clear from that photo. Get in touch and ask for some nicer photos, its worth a try is she far away?