Can I ask again about a postdoc position after a year has elapsed? Last year I sent an email to a professor to ask her about a postdoc position, and she showed her interest in my work but didn't have a grant. She told me that she will inform me in the case of having some grants. Is it appropriate to send her again to ask about grants again? Or I must wait until she will send me any information?
You can certainly ask again after a year (or less, perhaps). She may have forgotten, or may just be busy. There shouldn't be any issue with such a mail. You might also use the mail to fill her in on what you've accomplished in the interim - briefly.