Are Agatha, the Kanto Elite-4 member no. 3. and Bertha, the Sinnoh Elite-4 member no. 2. sisters? Well, lets look at the facts first:
Names
Their Japanese names are only one letter apart, Kikuko being Agatha's Japanese name, and Kikuno being Bertha's.
In English, their names are both 6 letters long, being A G A T H A and B E R T H A, and they both end in the syllable "tha".
Position
Both are very powerful trainers in their own right. They are both members of the Elite-4 of a league, and both have very powerful Pokemon.
Look
They both look very similar, being of the same height, hair-style, and sharing the same eye-colour (brown, since you ask). Also, if you dye Bertha's hair yellow, there is a definite resemblance to Agatha.
Pokemon
Bertha's team: Lv. 55 Quagsire, Lv. 55 Whiscash, Lv 56 Hippowdon, Lv 57 Sudowoodo, Lv 59 Golem
Agatha's R/B/Y Team: Lv. 55 Haunter, Lv. 56 Gengar, Lv. 56 Golbat, Lv. 58 Arbok, Lv 60 Gengar
Agatha's Fr/Lg Team: Lv. 53 Haunter, Lv. 54 Gengar, Lv. 54 Golbat, Lv. 56 Arbok, Lv. 58 Gengar
Agatha's Fr/Lg rematch team: Lv. 65 Misdreavus, Lv. 66 Gengar, Lv. 66 Crobat, Lv. 68 Arbok, Lv. 70 Gengar
Agatha's Stadium R1 team*: Haunter, Golbat, Arbok, Muk, Venusaur, Gengar
Agatha's Stadium R2 team*: Jynx, Alakazam, Arbok, Gyarados, Venusaur, Gengar
Note the level similarities between some of Agatha's teams, and Bertha's team, in particular Agatha's original R/B/Y team.
So, what do you think? Are they indeed sisters? If so, what happened? How did Agatha come to Kanto, and become Prof. Oak's amour? Why did Bertha remain in Sinnoh? What caused the two to be split up? And, later in life, why has Agatha's relationship with prof. Oak soured? Why has Agatha become so bitter compared to her possible sister, Bertha? And what part does Bertha play in Agatha's life? Speculate on this sister confusion here!
* The Stadium teams are set at level 50. If one of your Pokemons levels is higher than 50, they are set to the level of your highest leveled Pokemon.