I was adopted in 1958 when I was 14 months old. I have finally found my birth mother and also that I had 2 half-brothers. They told me that mom had had another baby when that she gave up for adoption in 1953. Well, I recently turned in my DNA etc. and one possible match really stands out, who matches many of the details I know about that earlier baby.. She also has turned in a DNA sample and we share 1845 cM's over 68 segments. Is there a strong possibility she is my half-sister?
At 1845cM according to the Shared cM project, it is 100% likely that this is your Grandparent Aunt / Half Sibling / Niece / Grandchild.
Given an age difference of 5 years, you can discount grandparent and grandchild. Aunt and niece are theoretically possible even with a 5 year difference, but half-sibling is very likely.