According to this fatwa (Arabic and Urdu are available) ghusl is not needed and in cases, assuming the woman was clean (has performed wudu' before the "intervention") she even doesn't have to perform wudu', because wudu' would only be necessary if she had some discharge, but this is a sign of pleasure.
Some quotes from this fatwa:
قال النووي رحمه الله : " إذا استدخلت منيا في قبلها أو دبرها : لم يلزمها الغسل "
Imam an-Nawawi said in Rawdat at-Talibyn روضة الطالبين: If she entered (made it enter somehow) some sperms in her foremost part or buttocks she doesn't need to do ghusl.
وقال البهوتي رحمه الله ـ في نواقض الوضوء ـ : " ( أَوْ وَطِئَ دُونَ الْفَرْجِ فَدَبَّ مَاؤُهُ فَدَخَلَ فَرْجَهَا ) ثُمَّ خَرَجَ : نَقَضَ ( أَوْ اسْتَدْخَلَتْهُ ) أَيْ : مَنِيَّ الرَّجُلِ ... ثُمَّ خَرَجَ نَقَضَ ) الْوُضُوءُ ؛ لِأَنَّهُ خَارِجٌ مِنْ السَّبِيلِ ، ( وَلَمْ يَجِبْ عَلَيْهَا الْغُسْلُ ) ؛ لِأَنَّهُ لَمْ يَخْرُجْ دَفْقًا بِشَهْوَةٍ ؛ ( فَإِنْ لَمْ يَخْرُجْ ... مِنْ ( الْمَنِيِّ شَيْءٌ : لَمْ يُنْقَضْ ) الْوُضُوءُ
Al-Bahoty said in his Kashf al-Qina' كشاف القناع-Chapter: The things that make wudu' void-:
If a man has intercourse without penetration and his sperm came out end entered her foremost part and came out or she let/made it enter and it leter came out than her wudu' is void, as the sperms came out of one of the "device". But she is not asked to perform ghusl, because the sperms didn't come out due to pleasure. If the sperms don't come out than her wudu' stays sound.
And Allah knows best!