Tensei Reijou to Suuki na Jinsei wo

Karen is reborn in another world, but she's entirely ordinary—no powers, no special skills, and no grand mission to accomplish. Fortunately, life is easy as a rich noble. Karen lives the good life until her mother completely forgets everything about her. When it's discovered that Karen is actually the child of an affair, she's banished from the family and forced to live on her own as a fourteen-year-old commoner! However, two years later, her family presents her with a chance to rejoin the ranks of the nobility under one condition: she must marry either the elderly, widowed margrave who lives on the frontier, or the dashing soldier who's seemingly destined for greatness. Which will she choose?

(Source: J-Novel Club)