One way to identify the spelling of a last name is to compare it with a list of common last names for that country.
It's always possible that the last name is not common, or the family intentionally spelt it in a unusual way, but a list of common names will often help.
For Poland, here's a ranked list of common last names in the 1990's.
There's also a list of all surnames at a Polish genealogy website.
Current list of surnames used in Poland (government resource, maintained).
The first one doesn't have much that looks useful (it's only the most common names) but some possibles from the second list:
- Dziubandowska (similar to the Dziubanowska that Luke sugggested)
- Dziubałtowska (the ł is pronounced like w in wall).
(plus other less likely spellings)
There's a site that maps the (modern) distribution of Polish names.
Putting those three names in the search box on that site, you can see the areas they come from, and this may either tie up with what you know or give you clues.
Another way to check would be with an online phone book (white pages) for the country, but Poland doesn't have one.
Dziubanovska is a rarer spelling that can be found in use (via Google), but it seems to be mostly people outside Poland (the w changes to a v).