Almost there and almost not / Linda Urban.

Enhanced descriptions from Syndetics:

From acclaimed author Linda Urban comes the funny, bittersweet story of a girl and her ghosts--and the welcoming home they find where they least expect it.

California Poppy has been dropped off, yet again, with an unsuspecting relative. This time it's her eccentric Great-Aunt Monica, a woman she's never even met. Aunt Monica has no idea what to do with an eleven-year-old, so she puts California to work researching their ancestor, the once-famous etiquette expert Eleanor Fontaine.

California soon discovers that Great-Great-Great Aunt Eleanor is...not exactly alive and well, but a ghost--and a super sensitive one at that. The grand dame bursts into clouds of dust whenever she loses her composure, which happens quite often. Still, an unexpected four-legged friend and some old-fashioned letter writing make this decidedly strange situation one that California can handle.

Just as California's starting to feel like she's found a place for herself, life turns upside-down yet again. Thankfully, this time she has some friends almost by her side...