Louisa Gabrielle Patterson was John Allan's second wife. They married on October 5, 1830. She disliked Edgar and was presumably part of the reason why Allan left Poe out of his will. Poe actually met the second Mrs. Allan only once, when John Allan was lying on his death bed. Around February 14, 1834, Edgar traveled to Richmond to see his ailing foster father. Mrs. Allan insisted that he did not wish to see Edgar and was too ill to see anyone. Edgar impetuously pushed his way past her, only to be scolded by John Allan who told him to leave.
N. H. Morison sent Ingram a letter in 1874 containing this note: ". . . it is a fact that Mrs. Allan, still living in Richmond, retains a bitter feeling towards him [Edgar]. Mr. N[eilson]. Poe thinks the trouble arose from the fact, that Edgar looked upon the young wife as an intruder into the family, who was pushing him out, & that he made his feelings known very distinctly as we might expect from his impulsive nature. This conduct on his part was deeply resented, & probably never forgiven, by both Mr. and Mrs. Allan" (Nathaniel Holmes Morison to John Henry Ingram, November 27, 1874, reprinted by John C. Miller, Building Poe Biography, pp. 51-52).
A confusing twist is added by Marie Louise Shew Houghton. In a letter
to J. H. Ingram, Mrs. Houghton claimed that "The day before Mrs. Poe died
I left to make some arrangements for her comfort. . . . She took from her
portfolio a worn letter and showed it to her husband. It expressed a desire
to see him, acknowledging that she alone had been the cause of his adopted
Father's neglect, out of Jealousy that Mr. Poe really was a relative by
blood to her husband. That if he would return to her at the end of her
year of mourning, she would provide for him, &c. This letter he answered
in score to her -- and she replied 'You was always a gentleman to me, always,
until now -- can you not forgive a fault so humbly acknowledged?'" (M.
L. S. Houghton to Ingram, March 28, 1875, Ingram Collection, item 210,
reprinted in Miller, p. 116). This account from Mrs. Houghton is extremely
unlikely, and demonstrates the difficulties in gathering information about
Poe even from those who knew him. Poe was clearly not a "relative by blood"
to John Allan. If Mrs. Allan ever wrote such a letter, it has apparently
not survived. When Ingram himself tried to contact Mrs. Allan, he was told
by Edward Valentine that the topic of Poe was "disagreeable to her" (Edward
Virginius Valentine to J. Ingram, May 4, 1875, Ingram Collection, item
222, noted in Miller, p. 171).